What Is the Structure of Human Populations?
The study of evolution is limited by its essentially stochastic nature. Even if we understand all the forces affecting the transmission of genes from one generation to the next, we cannot predict the future genetic constitution of a population and we cannot reconstruct all aspects of the past. The phrase “cannot predict” is to be taken in the same sense as when we decline to predict whether a toss of a fair coin will result in a head or a tail. We may be content to assign a probability of one half to each outcome, but the inherent uncertainty in the tossing process is widely acknowledged and even serves as the basis for deciding elections in the case of equal numbers of votes for each of two candidates. The possibility of studying the physics of coin tossing to such a degree that the outcome can be predicted with certainty is rejected, and biological processes such as meiosis are very much more complicated. Our theories of evolution are designed to apply on the average or to give probabilities to sets of outcomes. Our data, however, are from specific outcomes. Our understanding of evolution must proceed from the single replicate of the process. We can no more construct a complete theory of a stochastic process from specific data than we can predict a specific outcome with certainty from our theory.
KeywordsMarker Allele Recombination Fraction Fair Coin Evolutionary Equilibrium Population Genetic Theory
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